Fine edged blade



oct. zo, 1931. ^T H FROST '1,827,872

FINE EDGED BLADE Filed Nov. 14, 1930 Patented Oct. 20, 193i UNITED STATES THOMAS H. FltiOST,l OF ClAIlltBRIDGE,r MASSACHUSETTS FINE 'Encan BLADE Application led November 14, 1930. Serial No. 495,657.

This invention relates to fine edged blades of ferrous alloys which may be hardened by the process of nitriding. In one aspect it comprises a novel blade of such alloy characterized by a plated unnitrided body portion and a narrow unplated nitrided area in which the cutting edge is included. In another aspect vit com rises an improved method of producing suc blades.

An important field of use of my invention is in the production of safety razor blades of the thin flexible type which are adapted for use in holders wherein they are clamped forsupport. In my prirapplications Ser.

No. 455,366, filed May 24, 1930, and Ser. No.

494,591 filed November 10, 1930, I have vdisclosed safety razor blades with nitrided cutting edges and in still another aspect the present invention constitutes a development or zo carrying forward of these earlier inventions.

The material I prefer to employ in the construction of the novel blade of my invention is a ferrous alloy containing a substantial amount of aluminum usually combined with chromium or molybdenum ortungsten. An

example of such alloy is the material commerclall known as nitralloy and, while this is suita le for manufacture of fine-e ed blades, any other ferrous alloy capable of e- 3o ing hardened by the process of nitriding may be used, being selected in accordance with the requirements of the particular blade under construction.

When such metal is exposed to ammonia fumes under conditions of high temperature it becomes nitrided upon its exposed surfaces. and an extremely hard brittle case is formed thereon which may extendslightly below the surface of the blank. Difficulty has been ex perienced heretofore in nitriding a flat blank on account of the fact that expansion ofthe 4 material takes place in the nitriding operation which tends to warp or distort it to an objectionable extent, moreover blades nitrided throughout their area are too brittle for practical purposes. This is particularly true of suchanarticle as aviexible safety razor blade which is commonly maintained in a position of pronounced curvature'when in 5o use andv must therefore becapable of with- Y' plating has been removed.

standing appreciable bending. A razor blade of completely nitrided material is likely to shatter when bent between the fingers and so become a menace to the user.

I have discovered that if the nitrided area is confined to a narrow zone including little more than the bevelled portion of the blank or the vertex of the cutting edge then the blade as a whole, on account of its softer body portion, is rendered durable and capable of such flexing assis commonly imposed upon safety razor blades. While the actual cutting edge of such a blade is extremely hard and brittle the more flexible, tougher body of the blade offsets the fragility of its cutting edge and supports the same while being positioned or subject to use. I have discovered that an improved blade of these desirable characteristics may be produced by plating the body of the blank with a metal which is 7o impervious to ammonia fumes and then removing the platingfrom the margin of the blank in the narrow zone included in the cutting edge so as to expose the ferrous alloy of the blank in this restricted area only. The nitriding operation is then carried out upon the blank thus prepared with the result that it is nitrided and hardened only in the narrow marginal zone or zones from which the Preferably, and as herein shown, the method of my invention is characterized by simultaneously removing the lating in a narrow zone and partially forming a cutting edge upon the blank. This can be conven- .iently done by rough bevelling the edge of the blank and thus 1n a single operation two important functions are achieved, i.. e.: the exposure of the ferrous alloy in the desired restricted area and the partial formation of the cutting edge. After the nitriding operation the blade may be ycompleted by further grinding or' sharpening operations upon its rough bevelled and nitrided edge.

An important feature of a blade produced as above outlined resides .in the fact that it is therebyV rendered rust-resistant throughout. This is because the plated surfaces ofthe blade upon the unnitrided portions thereof are protected by the plating itself which may be of a non-ferrous, non-corrosive metal such for example as silver, copper, or tin, whereas the nitriding operation upon the exposed and unplated portions of the blade imparts to them all the rust-resistant properties of a high chromium steel. The latter property of` nitralloy andsimilar ferrousv alloys has been recognized heretofore but this characteristic has not been heretofore utilized in the construction of fine-edged blades which are@ rustresistant throughout. This feature is of eX- treme importance as applied to safety razor blades which are frequently moistened and imperfectly or hastily dried.

Another advantage incident to a blade of this character arises from the ornamental and attractive finish Ywhich the plating imparts to the blade. For example, a thin, plating ofsilver is adequate to protect the body of the blade from the nitriding action and the silver-plated surface which results in the finished blade` is extremely attractive and ornamental as a finish. Therefore, in carrying out the method of my invention, the single step of plating the blank is useful both in defining the unnitrided portions of theblade and in supplying a superior finish.

Still another advantage of the present invention resides in the fact that it can be applied to the manufacture of blades in strip form. Under such conditions the contour of the blades or of rthe blade blanks may be` outlined in strip stock of a nitridable ferrous alloy. The strip may then be plated and subsequently rough-ground in strip form which, from a manufacturing standpoint7 is an advantageous manner of carrying out these steps. The plated and rough ground blanks may then be nitrided either in the strip or as separated into individual blanks.

These and other features of my invention will be best understood and appreciated from the following description of a preferred manner of applying it to the manufacture of safety razor blades as illustrated in the accompanying drawings, in which: 'Y

Fig. 1 is a view in perspective of strip metal in which the blades have been outlined.

Fig. 2 is a similar view of the plated strip.

Fig. 3 is a similar view of the plated strip after the rough grindingstep has been carried out.

Fig. 4 isa view in perspective of a stack of blanks ready for the nitriding step.

Fig. 5 is a sectional view on the line 5-5 of Fig. 4, and

Fig. 6 is a view in perspective of' a finished blade.

In manufacturing safety razor blades by the method of my invention the blanks or blade blanks 10 are first outlined in strip'- form. As shown in Fig. 1 this may be done by punching or dieing out suitable notches and perforations in 'a continuous strip or ribbon of nitralloy or other ferrousv nitridable alloy whichl may be procured, rolled to the desired thickness. As herein shown each blade blank is provided ywith an internal aperture 12 in the shape of a slot intersecting spaced recesses and with cut-out portions which forms corner notches 14 to relieve the finished blade of corner-cap pressure. The strip may be scored or otherwise m'arked to set off one blank from the next but the step of outlining the blades and the ensuing steps of the method are carried out with the material'in strip form.

The material employed for the production of the blank may advantageously .be of either of the following analyses:

, Anal sis Anal sis Element (Ag (Bg Carbon 36 23 Mnnzanesn 51 51 Silicon 27 2() Aluminum 1, 23 1. 24 Chnrminm 1. 49 1. 58 Sulphur. 010 .011 Phosphorus 013 011 Molybdenum 18 20 The analyses above set forth aretypical of a satisfactory nitralloy material for the manufacture of fine edged blades but nitralloy of other similar analyses may be successfully used.

The next step in carrying out the method of my invent-ion consists in plating or coating the blade strip with a non-ferrous metal. I have found that tin, copper, silver nickel, chromium and possibly other metals are suitable for this coating, and while any metal which is impervious to ammonia fumes would be satisfactory, I prefer to employ a silver-plating partly on account of the superior finish which is derived therefrom in the finished blades. In electro-plating the blade strip the entire surface of the strip is coated together with its exterior marginal egges and the interior edges of the aperture 1 The next step consists in removing the plating from the narrow marginal zone of the stripin which the cutting edge is to be' formed and this may be effected to best acl-- vantage by rough grinding the edges of the strip to form the bevel 16. vThis stefp as alblanks are stacked flatwise and secured in such position. Any convenient number of blanks maybe stacked and preferably these are clamped as suggested in Fig. 4 between a thick bottom plate 20 and a thick top plate 22 secured together by clamping bolts 34 which pass through the plates and through the apertures of the blade blanks. v Having arranged the blanks in stack form as above outlined with or without the addition of spacin` shims the stack is placed in a furnace and su jected to the actionof ammonia gas for a predetermined interval of time and-at a proper temperature for the nitriding requirements of the blade. Satisfactory blades may be produced from nitralloy of the analyses above set forth by subjecting the stack to a temperatureof about 900 F. to 950 F. or thereabouts for a period of two hours. Under these circumstances the exposed bevel edges of the blades will have a hard nitrided A case formed thereon but nowhere else, while the blade as a whole will be maintained in flat condition in the stack. The case may extend entirely through the material of the bevel or it may extend merely a few thousandths of an inch below the surface thereof but in any case the vertex of the blade is completely nitrided.

After the conclusion of the nitriding step the stack is removed from the furnace and allowed to cool thereupon the clamping bolts 24 may be released and the blades separated. The hardened nitrided case permits the rough bevel 16 of the blank to be finish ground, honed and stropped to produce the smooth bevel 17 of the finished bladev 11 shown in Fig. 6. The silver plated surface of the blade presenfs at all times an attractive finish and may be rendered brilliant by a slight bufling operation. As already` intimated the elongated narrow nitrided zone defined by the bevel 17 in the finished blade is of extreme hardness and although it is also brittle it is carried and distributed along the unnitrided soft and flexible body of f'he blade in such a manner that, as a complete article, the blade affords satisfactory service.

Having thus described my invention what I claimas new and wish to secure by Letters Paten-t of the United States is- 1. A fine edged blade of a nitridable alloy, bevelled to form a cutting edge, nitrided only in a n'arrow zone defined by the bevel and plated throughout the remainder of its surace.

2. A fine edged blade of a nitridable alloy, having a plated body limited in its area by a bevelled edge portion and being nitrided in such bevelled portion only.

3. A fine edged blade of a nitridable alloy, having supplementary plated and nitrided areas, whereby the whole surface of the blade is rendered rust-resistant.

4. A ne edged blade of a nitridable alloy,

having fiat plated areas and supplementary bevelled areas which are nitrided, whereby the whole surface of the blade is rendered rust-resistant.

5. A fine edged blade of a nitridable alloy, bevelled to form a cutting edge, having a non-ferrous plating upon its body and being nitrided in a narrow zone which is substantially coextensive with its bevelled cutting edge.

A fine edged blade of a nitridable alloy, internally apertured to receive blade positioningmeans and being plated upon its surface and the marginal edges of its aperture, and having an unplated bevelled and nitrided cutting edge.

7 The method of making fine edged blades, which consists in producing a flat blank of a nitridable ferrous alloy plated upon its surfaces except in a narrow marginal portion thereof, nitriding said marginal portion and reducing it to a cutting edge.

8. The method of making fine edged blades, which consists in producing a blank of a nitridable ferrous alloy, forming an ornamental and protective plating onthe surfaces thereof, bevelling a marginal portion of the blankto remove the plating in a narrow zone, and nitriding the portion of the blank thus exposed.

9. The method of making fine edged blades, which consists in defining the outline of the blade in sheet stock of nitridable ferrous alloy, plating the entire area so defined, removing the plating in a narrow marginal zone and reducing the thickness of the blank in the same zone, nitriding the stock thus exposed, and then finish grinding to produce a cutting edge in nitrided stock.

10. The method of making fine edged blades, which consists in producing a blank having an internal aperture from a nitridable ferrous alloy, plating the surface of the blank including the marginal edges of its aperture, bevelling an outer edge of the blank to remove the plating, and then nitriding the ferrous alloy thus exposed.

11. The method 'of making fine edged blades, which consists in producing a blade blank in ferrous nitridable alloy, rendering the entire blank rust-resistant by plating the surface thereof and nitriding the outer edge, and forming a'cutting edge in the nitrided portion of the blank.

12. The method of making fine edged blades, which consists in outlining the blade blanks in a strip of nitridable ferrous alloy, plating the strip, rough grinding the margin of the plated strip to remove the plating and partially form a. cutting edge, separating the strip into individual blanks, nitriding the bevelled portionsl of the blanks, and finish grinding the nitrided portions to complete the blades. f

13. A fine edged blade of a nitridable ferrous alloy, having a silver plated body lmited in its area by abevelled edge portion and being nitrided in' such bevelled portion only.

14. A fine .edged blade of a nitridable ferrous alloy, bevelled to form a. cutting edge, having a nickel plating upon its body and being nitrided in a narrow zone which is substantially -coextensive with its bevelled cuttin edge. A

igned at Boston,' Massachusetts, this 12th day of November, 1930.

A THOS H. FROST. 

